The present invention relates to a device for linearly conveying sheet-like products, fed with a first conveyor having a first speed, to a second conveyor or, apparatus having a second speed different from the first speed.
A prior art device of the above-described type includes a conveyor belt, driven with a constant speed, for conveying metal sheets stacked at one location to a piling table spaced from the one location. After the metal sheets leave the conveyor belt, they hit a stop surface and thereby are brought to a stop, with their speed being thus reduced to zero, to be deposited on the piling table.
One of the drawbacks of this known conveying device consists in that the deposited sheet may damage the upper surface of the uppermost sheet of a stack already formed on the piling table. Further, the deceleration to zero speed or braking of the deposited sheets are not easily reproducible for the following sheets. This is because the stackable on the piling table sheets often hit the stop surface at a high speed, so that a back pressure of the braking buffer or the like is applied to the sheets.
EP 0408 893A1 discloses a stacking device for conveying sheets fed at a constant speed, which comprises pull-up rollers arranged side by side for accelerating sheets, which are cut-off by a rotational cutter, in order to space a rear edge of an already cut-off sheet from the front edge of the following sheet that is being cut-off. In the conveying direction of the sheets downstream of the pull-up rollers, there is provided a suction braking table including a conveying suction belt having a displacement speed lower than the speed of the pull-up rollers. After the sheets leave the pull-up rollers, they are received on the suction belt having a reduced speed in comparison with that of the pull-up rollers. It is to be pointed out that both the acceleration of the sheets by the pull-up rollers and the deceleration of the sheets by the suction braking table can result in a damage of the sheets.
German patent No. 2,348,320 describes a stacking device comprising a plurality of suction conveying rollers, spaced from each other a distance smaller than the length of the conveying sheets, and a plurality of suspended strips, which are subjected to air blasts, for feeding flexible sheets to a piling table. Before stacking, the sheets are transferred to the suction conveying rollers, which have a rotational speed lower than the sheet conveying speed, so that the speed of the sheets is reduced to a lower stacking speed as a result of a sliding friction or slippage. However, this device also does not eliminate a possibility of sheet damage.
The prior art discloses also a device for sluicing previously inspected sheets removed from a treatment apparatus or a conveyor. The sluicing device is so formed that the inspected sheet is inserted into the position of the following sheet taken off for inspection. The known sluicing device comprises a ramp-like conveying belt for supporting the sheet in its wait position. Immediately, after taking off of the following sheet, a coupling force lockingly connects the conveying belt with the drive of the conveyor, and the previous sheet is inserted into the "gap" in the conveyor. During acceleration of the previous sheet and during its insertion into the sheet stream conveyed by the conveyor, the relative movement between the sheet and conveying medium may cause damage of the sheets. Further, the known sluicing device does not insure a very accurate sluicing reproducibility. Considering the customary speed and the conventional spacing of the conveyed articles from one another, the sluicing accuracy should lie within a range of 20-100 millisecond. If this accuracy cannot be achieved, the sheets overlap each other, which leads to a damage and disturbances of the conveyor drive. Because of the use of the force-locking connection and because of an associated therewith change of the sluicing time, it is not possible to use the device for an extended period of time, while insuring an accurate sluicing reproducibility. Instead of a coupling connection, a lowering mechanism can be used for sluicing the sheets with a declining drive force and for inserting the sheets into the gaps in the conveyor. These measures, however, hardly permit a damage-free sluicing with the required accuracy.
The prior art also discloses a sheet loading device for a treatment apparatus. The known loading device comprises a flat conveying belt onto which sheets are fed one after another with a high speed. Downstream of the conveying belt, there are provided metal rails on which the conveyed sheets slide. A far away region of the metal rails defines or is formed as a braking region having braking surfaces along which the sheet slides with a reduced speed. The braking surfaces may comprise metal attracting magnets or suction opening. Here also a mechanical damage of sheets takes place. Further, it is not possible to insure transfer of the sheets to the handling or treatment apparatus in a predetermined manner and with an accurate reproducibility.
Accordingly, an object of the invention is a device of types described above which would insure damage-free feeding or delivery of sheet-like products to and from sheet handling apparatuses and arrangements with a precise reproducibility of the kinematic processes.